1. Field of the Invention
This invention relates to the manufacture of a lithium electrochemical cell or battery, and more particularly to a new and improved method of preparing silver vanadium oxide composite cathode material for high energy density batteries.
2. Prior Art
A solid cathode, liquid organic electrolyte lithium anode cell or battery has been used as the power source for implantable medical devices. The cathode of such a cell, or other alkali metal anode battery or cell, may have as active material carbon fluoride, a metal oxide, a metal oxide bronze such as silver vanadium oxide, or other suitable material as disclosed in U.S. Pat. No. 4,830,940 to Keister et al., which patent is assigned to the assignee of the present invention and which patent is incorporated herein by reference.
Typically, cathode material containing silver vanadium oxide, for use in a lithium cell or battery, may be prepared in two steps by thermally decomposing a vanadium salt to produce vanadium pentoxide. A decomposable metal salt, preferably containing silver, is added to the vanadium pentoxide and the mixture is oven-dried. Following drying, the mixture is mixed and ground to ensure homogeneity and is subsequently baked for a final heating/decomposition period. Depending on the starting materials used, this heating/decomposition period can result in the release of toxic by-product gases. For example, if silver nitrate is used as the silver source, nitrous oxide type gases may be formed. Upon cooling the baked material, it is blended with appropriate amounts of graphite powder to enhance conductivity, and binder material, and then pressed to form the cathode. Such a method is described in more detail in U.S. Pat. No. 4,310,609 to Liang et al., which patent is assigned to the assignee of the present invention and which patent is incorporated herein by reference.
Vanadium pentoxide (V.sub.2 O.sub.5) gels, produced by the "sol-gel process", have been known in the art of material sciences (see for Example, J. Livage, Chem. Mater 3:578-593, 1991). Sol-gel synthesis of transition metal oxides may be accomplished by introducing a material into solution and under specific conditions, such as pH, elevated temperatures, or solvent levels, a gel is formed from the species of interest. Typically the synthesis of V.sub.2 O.sub.5 gels may involve protonation accomplished by adding an acid to a vanadium salt solution or by passing the solution through an ion-exchange resin. Preparation of V.sub.2 O.sub.5 gels by the sol-gel process may result in reduction of vanadium resulting in mixed-valence properties of the gels; and differences in structural orientation or character of the composition resulting in a change in physical and/or electrochemical properties. Thus, utilization of the sol-gel method, as an alternate preparation technique to other chemical processes currently used for cathode formation, allows generation of novel properties of the material and provides different ways of preparing cathodes.
References relating to the art of the sol-gel process, and disclosing V.sub.2 O.sub.5 gels, include the following:
J. Livage et al. "Chem. Mater." 3:578-593, 1991, reviews synthesis of V.sub.2 O.sub.5 gels by the sol-gel process, structure studies of the resultant gels, electronic and ionic properties of vanadium oxide thin films deposited from gels, and intercalation of metal or molecular species into V.sub.2 O.sub.5 gels.
E. Andrukaitis et al "J. Power Sources", 26:475-482, 1989, describe lithium insertion into electrodes composed of V.sub.2 O.sub.5 deposits formed by either electrophoretic deposition of ammonium hexavanadate monohydrate, or by spreading hydrated V.sub.2 O.sub.5 gels followed by heating at elevated temperatures.
L. Znaidi et al. "Mat. Res. Bull.", 24:1501-1514, 1989, describe the preparation of vanadium bronzes using the sol-gel process with the intercalation of sodium or silver ions, and structural studies of the resultant vanadium bronzes.